Numerous types of inspection processes require specialized sources of light to provide proper illumination of a part or features to be inspected. One typical application of specialized light sources for inspection processes involves the inspection of printed circuit boards at an intermediate step in their fabrication. Electrical components have pins or electrical leads which are inserted through holes in the board by automated equipment. After insertion, the leads may be crimped by automated machinery and are thereafter soldered to the printed circuit on the board. For any of various reasons, the leads may not be properly inserted through the holes in the board, and it is therefore necessary to inspect the leads after the insertion process to assure that the leads properly extend through the board and/or are properly crimped. Various systems, typically employing video cameras are used to automatically inspect the leads after they have been inserted. In order to properly view the leads with "artificial" vision system, it is necessary to illuminate the leads in a manner such that light is reflected from the leads to the camera.
Complicating the goal of proper illumination of printed circuit boards, and other objects having similar features, is the fact that the boards are of different sizes, may be held in various kinds of attitudes by automated inspection equipment and have different types of leads crimped in various manners at different attitudes using different techniques. It is, therefore, important to provide an illumination device which illuminates as wide of an area as possible while, at the same time, is of relatively low cost and easily set up to accommodate changing product inspection applications.
In inspection applications of the type described above, it is also necessary to achieve an illumination condition in which the electrical leads are illuminated in relatively high contrast relative to the board. In the past, others have employed bundles of optical fibers illuminating a spherical lens to provide the necessary illumination. This prior approach was relatively position-sensitive in terms of its ability to thoroughly illuminate given surface features. The problem of position sensitivity can be overcome, in part, by employing a larger light source, but this alternative is undesirable because of its expense.
There is, therefore, a need in the art for an illumination device which employs a relatively modest size light source which can easily and quickly be set up to accommodate varying inspection illumination requirements, while, at the same time, is not sensitive to position and provides a relatively constant intensity of light over a substantial distance from the light source.